Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Abstract

AbstractOrganisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular adaptations to thermoregulate during hot and cold conditions. However, our knowledge if and how selection acts on thermoregulation and the potential for evolutionary responses is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we use thermal imaging to quantify selection and genetic variation in thermoregulation in ostriches (Struthio camelus), the world’s largest bird species that is regularly exposed to increasingly volatile temperatures. We found that females that are better at regulating their head temperatures had higher egg-laying rates under hotter conditions. Thermoregulatory capacity was both heritable and showed signatures of local adaptation. Females originating from populations exposed to more unpredictable climates were better at regulating their head temperatures in response to temperature fluctuations. Together these results reveal that past and present evolutionary processes have shaped genetic variation in thermoregulatory capacity, which appears to protect critical organs, such as the brain, from extreme temperatures during reproduction.Impact SummaryLarge animals inhabiting extreme thermal environments, such as deserts, are predicted to be particularly vulnerable to the sustained heat waves expected in their future climate. However, previous research on the evolution of thermoregulation has focused on the effect of increasing temperatures on survival in ectotherms. Here we study the ostrich (Struthio camelus), the world’s largest bird, that inhabits some of the hottest and driest regions on Earth. We show that the ability of females to reproduce during hot conditions is associated with their thermoregulatory capacity. Furthermore, variation in thermoregulation is heritable and related to past climatic conditions: Females from populations originating from parts of Africa with more extreme temperature fluctuations were better able to thermoregulate, indicating local adaptation to different climatic conditions. Together, these results suggest that thermoregulation in this large desert bird has evolved in response to past climatic conditions, remains genetically variable and is currently under selection due to its effect on reproduction.